Liquid crystal display (LCD) devices are well known and are useful in a number of applications where a light weight, low-power, flat-panel display is desired. Typically, these devices comprise a pair of sheet-like, glass substrate elements or "half-cells" overlying one another with liquid crystal material confined between the glass substrates. The substrates are sealed at their periphery with a sealant to form the cell or device. Transparent electrodes are generally applied to the interior surface of the substrates to allow the application of an electric field at various points on the substrates thereby forming addressable pixel areas on the display.
Various types of liquid crystal materials are known in the art and are useful in devices referred to as twisted nematic (TN), super twisted nematic (STN) and ferroelectric (FE) display devices. The ferroelectric liquid crystals are particularly useful due to their bistable characteristics, fast switching times, and good contrast in large area displays. Ferroelectric liquid crystals are comprised of molecules having a polarization vector that aligns with an applied electric field. Thus, the application of an electric field ("field-on condition") causes these liquid crystal molecules to orient in a characteristic way. Because they are bistable materials, they remain as oriented by the field even after the orienting electric field is removed ("field-off condition") thereby reducing power consumption. Application of a field of different polarity can re-orient the liquid crystal materials to a different orientation characteristic of the field. Because the liquid crystals affect light differently in different orientations, they can be made to effectively switch picture elements (pixels) in a display device on and off to display information as is well known in the art. Ferroelectric liquid crystal materials and display devices are described in U.S. Pat. No. 4,367,924 entitled "Chiral Smectic C or H Liquid Crystal Electro-Optical Device" and U.S. Pat. No. 4,563,059 entitled "Surface Stabilized Ferroelectric Liquid Crystal Devices".
LCD devices can be made with either flexible or rigid optically transparent non-birefringent substrates. If rigid substrates are used, the substrates must be optically flat. This is because small variations in the separation of the two substrates affect the electric field created in the LCD material, which in turn affects the performance of the LCD device.
If flexible substrates are used to form the LCD device, the substrates need not be optically flat because the substrates can bend to conform to each other. Flexible substrates are, however, more likely to delaminate than rigid substrates. Delamination results in air entering the LCD cell, which creates air bubbles in the LCD material, thereby changing the spacing of the substrates. Delamination also allows moisture to enter the LCD cell, which can result in the creation of dead zones, i.e., defective pixels, within the LCD cell.
Delamination can be prevented by applying epoxy between the interior substrates. However, great care must be taken during the application of the epoxy to ensure that its thickness does not affect the spacing between the substrates, which can lower the contrast of the LCD cell. Furthermore, the epoxy must be of a type that will not chemically react with the liquid crystal material.
It would be desirable to have an LCD device which combines the advantages of flexible substrates with the advantages of rigid substrates, without the attendant disadvantages of either.